Source/JavaScriptCore/bytecode/EvalCodeCache.h

/*
 * Copyright (C) 2008, 2009 Apple Inc. All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * 1.  Redistributions of source code must retain the above copyright
 *     notice, this list of conditions and the following disclaimer.
 * 2.  Redistributions in binary form must reproduce the above copyright
 *     notice, this list of conditions and the following disclaimer in the
 *     documentation and/or other materials provided with the distribution.
 * 3.  Neither the name of Apple Inc. ("Apple") nor the names of
 *     its contributors may be used to endorse or promote products derived
 *     from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY APPLE AND ITS CONTRIBUTORS "AS IS" AND ANY
 * EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
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 */

#ifndef EvalCodeCache_h
#define EvalCodeCache_h

#include "Executable.h"
#include "JSGlobalObject.h"
#include "JSScope.h"
#include "Options.h"
#include "SourceCode.h"
#include "SourceCodeKey.h"
#include <wtf/HashMap.h>
#include <wtf/RefPtr.h>
#include <wtf/text/StringHash.h>

namespace JSC {

    class SlotVisitor;

    class EvalCodeCache {
    public:
        // Specialized cache key (compared with SourceCodeKey) for eval code cache.
        class CacheKey {
        public:
            CacheKey(const String& source, DerivedContextType derivedContextType, EvalContextType evalContextType, bool isArrowFunctionContext)
                : m_source(source.impl())
                , m_flags(SourceCodeType::EvalType, JSParserBuiltinMode::NotBuiltin, JSParserStrictMode::NotStrict, derivedContextType, evalContextType, isArrowFunctionContext)
            {
            }

            CacheKey(WTF::HashTableDeletedValueType)
                : m_source(WTF::HashTableDeletedValue)
            {
            }

            CacheKey() = default;

            unsigned hash() const { return m_source->hash(); }

            bool isEmptyValue() const { return !m_source; }

            bool operator==(const CacheKey& other) const
            {
                return m_source == other.m_source && m_flags == other.m_flags;
            }

            bool isHashTableDeletedValue() const { return m_source.isHashTableDeletedValue(); }

            struct Hash {
                static unsigned hash(const CacheKey& key)
                {
                    return key.hash();
                }
                static bool equal(const CacheKey& lhs, const CacheKey& rhs)
                {
                    return StringHash::equal(lhs.m_source, rhs.m_source) && lhs.m_flags == rhs.m_flags;
                }
                static const bool safeToCompareToEmptyOrDeleted = false;
            };

            typedef SimpleClassHashTraits<CacheKey> HashTraits;

        private:
            RefPtr<StringImpl> m_source;
            SourceCodeFlags m_flags;
        };

        EvalExecutable* tryGet(bool inStrictContext, const String& evalSource, DerivedContextType derivedContextType, EvalContextType evalContextType, bool isArrowFunctionContext, JSScope* scope)
        {
            if (isCacheable(inStrictContext, evalSource, scope)) {
                ASSERT(!inStrictContext);
                return m_cacheMap.fastGet(CacheKey(evalSource, derivedContextType, evalContextType, isArrowFunctionContext)).get();
            }
            return nullptr;
        }
        
        EvalExecutable* getSlow(ExecState* exec, JSCell* owner, bool inStrictContext, DerivedContextType derivedContextType, EvalContextType evalContextType, bool isArrowFunctionContext, const String& evalSource, JSScope* scope)
        {
            VariableEnvironment variablesUnderTDZ;
            JSScope::collectVariablesUnderTDZ(scope, variablesUnderTDZ);
            EvalExecutable* evalExecutable = EvalExecutable::create(exec, makeSource(evalSource), inStrictContext, derivedContextType, isArrowFunctionContext, evalContextType, &variablesUnderTDZ);
            if (!evalExecutable)
                return nullptr;

            if (isCacheable(inStrictContext, evalSource, scope) && m_cacheMap.size() < maxCacheEntries) {
                ASSERT(!inStrictContext);
                m_cacheMap.set(CacheKey(evalSource, derivedContextType, evalContextType, isArrowFunctionContext), WriteBarrier<EvalExecutable>(exec->vm(), owner, evalExecutable));
            }
            
            return evalExecutable;
        }

        bool isEmpty() const { return m_cacheMap.isEmpty(); }

        void visitAggregate(SlotVisitor&);

        void clear()
        {
            m_cacheMap.clear();
        }

    private:
        ALWAYS_INLINE bool isCacheableScope(JSScope* scope)
        {
            return scope->isGlobalLexicalEnvironment() || scope->isFunctionNameScopeObject() || scope->isVarScope();
        }

        ALWAYS_INLINE bool isCacheable(bool inStrictContext, const String& evalSource, JSScope* scope)
        {
            // If eval() is called and it has access to a lexical scope, we can't soundly cache it.
            // If the eval() only has access to the "var" scope, then we can cache it.
            return !inStrictContext 
                && static_cast<size_t>(evalSource.length()) < Options::maximumEvalCacheableSourceLength()
                && isCacheableScope(scope);
        }
        static const int maxCacheEntries = 64;

        typedef HashMap<CacheKey, WriteBarrier<EvalExecutable>, CacheKey::Hash, CacheKey::HashTraits> EvalCacheMap;
        EvalCacheMap m_cacheMap;
    };

} // namespace JSC

#endif // EvalCodeCache_h